FIELD OF THE INVENTION
The invention is in the field of semiconductors. More specifically, the invention pertains to an SOI-FET (SOI: "Silicon-On-Insulator") having a gate provided on an insulating layer, source and drain zones of one conductivity type which are arranged on an insulator with respect to the gate, and having a semiconductor zone ("body") of the other conductivity type which is arranged between the source and drain zones.
Thin SOI transistors for fast low-voltage ICs have become increasingly important in recent times (see, for example, the paper "Thin-Film SOI Emerges" by Michael L. Alles in IEEE Spectrum, June 1997, pages 37-45). If the gate electrode is capacitively coupled to the semiconductor zone between source and drain zones, the semiconductor zone being referred to as "body", in such SOI-FETs, then the reverse current is considerably reduced in the off state. This relationship is illustrated in FIG. 6, in which the gate-source voltage U.sub.GS is plotted in V on the abscissa and the logarithm of the source-drain current I.sub.SD is plotted on the ordinate. At a point a.sub.1, a curve (a) illustrates the reverse current without capacitive coupling between the gate electrode and the "body", while at a point b.sub.1, a curve (b) specifies the reverse current with capacitive coupling between gate electrode and "body". It can immediately be seen from the diagram of FIG. 6 that the reverse current becomes smaller with capacitive coupling between the gate electrode and the "body".
FIG. 7 illustrates a circuit diagram of an SOI-FET 1 having a capacitor C.sub.K for capacitive coupling between a gate electrode G and the "body" B of the SOI-FET 1 between a source electrode S and a drain electrode D. If the gate electrode G is directly connected to the "body" B then a connection indicated by dashed lines is present.
The coupling capacitance of the capacitor C.sub.K should intrinsically be as large as possible since a high coupling capacitance means a low reverse current. That is to say the reverse current becomes smaller, the greater the coupling capacitance between the gate electrode G and the "body" B is.
However, capacitances are generally proportional to the area of the electrodes that form them. Accordingly, an intrinsically desired large coupling capacitance necessitates a large area, which is precisely the opposite of what is striven for in the context of integrated circuits with the generally necessary miniaturization of circuits.